Metals and metal alloys are present in some shape or form in nearly every facet of our lives. Many metals and metal alloys are subject to corrosion that causes these metals and metal alloys to lose their structural integrity. As such, methods have been developed to detect the presence of corrosion and to inhibit corrosion.
For example, color or fluorescent indicators have been combined directly with liquid coating materials, such as paints, temporary coating materials, etc., to indicate corrosion, based on the pH or electrical changes associated with corrosion, when the coating materials are applied to corrosion containing surfaces. However, problems, such as the solubility of the indicator in a coating material and/or chemical reactions, interference with the coating material, etc., can arise when an indicator is combined directly with a coating material. Another problem is that the indicator may not be compatible with the coating material and may negatively affect the coating capability of the coating material when the indicator is combined directly with the coating material.
Nondestructive evaluation methods, such as X-ray techniques, including X-ray scattering and X-ray absorption spectroscopy, are sometimes used to detect the presence of corrosion under coatings. However, the resolution and/or sensitivity of such methods can make it difficult to detect corrosion in its early stages. In addition, these techniques can be excessively time intensive and typically require bulky, expensive equipment.
Corrosion inhibitors have also been combined directly with coating materials. However, directly combining a corrosion inhibitor with a coating material can lead to compatibility issues between the corrosion inhibitor and the coating material that can negatively affect the coating properties and/or reduce the corrosion protection capability of the corrosion inhibitor.
Microcapsules, containing a corrosion inhibitor, have been added to protective coatings, such as paints, that are applied to metal surfaces and dried. The microcapsules have a frangible wall material that confines the corrosion inhibitor until the dried coating is subjected to a mechanical force, due to an impact, abrasion, or cutting, etc., sufficient to fracture and fragment the wall material. When the fracture occurs, the corrosion inhibitor leaks into and spreads through damage sites to provide corrosion protection. However, there can be other defects in a coating applied to a surface besides those caused by mechanical forces, such as air bubbles occurring in the coating, pin holes occurring in the coating, uneven coating thickness, poor coating adhesion to an unclean metal substrate, poor coating adhesion at corners, etc., that can result in corrosion of the metal. In addition, the frangible capsules may include a dye that marks the damage sites for notice and possible detailed repair, but the dye is only released in response to the fracture of the capsules and indicates mechanical damage that could possibly, but not necessarily, result in corrosion.